The present invention relates generally to aspirating face seals for rotor and stator assemblies and, more particularly, to a rotor and stator assembly with an aspirating face seal having seal teeth.
Aspirating face seals are used to minimize leakage through a gap between two components and from a higher pressure area to a lower pressure area. Such seals have been disclosed for use in rotating machinery, including, but not limited to, turbomachinery such as gas turbine engines used for power generation and for aircraft and marine propulsion. Aspirating face seals are designed to minimize leakage of a fluid such compressed air or combustion gases between a rotor and a stator in gas turbine engines.
Conventional aspirating face seals typically have the rotor configured as oppositely facing first and second seal elements, with the first seal element either being attached to, or being a monolithic portion of, the rotor. Likewise, such seals typically have the stator configured as the second seal element, with the second seal element either being attached to, or being a monolithic portion of, the stator. The first and second seal elements are generally annular, generally perpendicular to the longitudinal axis of the rotor, generally opposing, axially spaced apart, and proximate each other. Typically, the first part and second elements together define a radially extending air bearing and a radially extending air dam positioned radially inward of the air bearing. An air bearing surface of the first element and an air dam surface of the first element generally lie in the same plane. The air bearing surface of the second element has a hole which is an outlet for a first passageway connecting the hole with air from a higher pressure side of the seal. The stator has a second passageway which carries air, which has passed the air dam from the higher pressure side of the seal, to a lower pressure side of the seal. Known seal designs have also included an aspirator tooth extending from the stator axially across, and radially inward of, the air dam, with the aspirator tooth having a tip spaced apart from and proximate the rotor. It is also important to note that aspirating face seal technology uses phrases such as xe2x80x9cair bearingxe2x80x9d, xe2x80x9cair damxe2x80x9d, and xe2x80x9cair flowxe2x80x9d, wherein it is understood that the word xe2x80x9cairxe2x80x9d is used to describe the working fluid of the seal. The working fluid of an aspirating face seal can include, without limitation, compressed air, combustion gases, and/or steam.
It is important to note that an aspirating face seal is a non-contacting seal in that the first and second parts of the seal are not suppose to touch but often do for short periods of time during which they experience what are known as rubs. Aspirating face seals generate significant heat and/or scratch rotor surfaces when seal rubs occur. It is, thus, desirable to minimize heat input into the rotating component and maintain a smooth surface flush. Excessive heat input into the rotor component can result in material degradation which in turn can lead to premature component crack initiation. A rough surface finish could result in excessive seal leakage and create a stress riser, which could also cause premature component crack initiation.
A gas turbine engine aspirating face seal includes a rotatable engine member and a stationary engine member and a leakage path therebetween. Annular generally planar rotatable and non-rotatable gas bearing face surfaces circumscribed about a centerline are operably associated the rotatable and non-rotatable engine members respectively. Radially inner and outer tooth rings axially extend away from a first one of the rotatable and non-rotatable gas bearing face surfaces across the leakage path and towards a second one of the gas bearing face surfaces. An annular plenum is located between the inner and outer tooth rings along the first one of the rotatable and non-rotatable gas bearing face surfaces. The inner and outer tooth rings have pointed ends proximate to the second one of the rotatable and non-rotatable gas bearing face surfaces. A pull off biasing means is incorporated for urging the inner and outer tooth rings axially away from the second one of the rotatable and non-rotatable gas bearing face surfaces.
In a first exemplary embodiment of the invention, the rotatable engine member is a rotor disk or the rotatable engine member is a side plate mounted the rotor disk and the non-rotatable engine member is mounted on a translatable cylindrical piston which is circumferentially continuous and axially movably supported on a stationary face seal support structure. The seal may incorporate an auxiliary seal disposed across the leakage path radially inwardly of the inner and outer tooth rings. The auxiliary seal includes an annular restrictor tooth radially spaced apart from and proximate to an annular seal land having an annular auxiliary seal surface circumscribed around the engine centerline.
The biasing means is operably disposed between the cylindrical piston and the stationary face seal support structure. The biasing means may include a plurality of circumferentially spaced apart coil springs disposed within circumferentially spaced apart spring chambers formed in part by radially extending static and axially movable flanges attached to the face seal support structure and the translatable cylindrical piston respectively. Alternatively, the biasing means may include a wave spring disposed in a continuous annular spring chamber formed in part by radially extending static and axially movable flanges attached to the face seal support structure and the translatable cylindrical piston respectively.
In a more particular embodiment of the invention, the face seal is incorporated in a turbine engine seal assembly between a relatively high pressure region and a relatively low pressure region at a juncture between the rotatable engine member and the stationary engine member. In a yet more particular embodiment of the invention, the stationary engine member depends from a turbine nozzle and supports an inducer which is operable to direct a portion of high pressure compressor discharge air across the high pressure region.